The present application relates to solid-state radio-frequency (RF) power amplifiers and, more particularly, to a novel cryogenically-cooled metal-oxide-semiconductor field-effect transistor (MOSFET) power amplifier cooled by liquid nitrogen (LN.sub.2) and the like.
Several uses exist for RF power amplifiers which can provide outputs in the 10 KW-100 KW power output range at frequencies on the order of 1-10 MHz. Among such uses are recovery of oil from oil shales and tar sands, in which large potential energy resources exist in an estimated 200 trillion oil barrel equivalents in the U.S. alone. It is necessary to heat the selected oil shale volume (which may be an in-situ mass of size on the order of 20 M.times.25 M.times.150 M) to temperatures on the order of 350.degree. C. Such temperatures can be obtained in these volumes by inducing in excess of a megawatt of RF power, in the frequency range 0.5-13.5 MHz, by means of several transmitters each having outputs of about 100 KW. These amplifiers would be operated continuously over several years, so that long life, reliability and high energy conversion efficiency would be mandatory. It is desired to provide high-efficiency cryogenically-cooled RF power amplifiers, utilizing liquid nitrogen-cooled MOSFETs with efficiency levels of at least 98 %.